Image forming screen utilizing electroluminescent,
ferroelectric and photcconductive materials



FERROELECTRIC AND PH Filed Oct. 28. 1963 51 E L LAYER Low CONDUCTIVITY GROJP THREE ELECTRODE mm n'mm-zmwwum:a wqrasu OPAQUE ELECTRODE 30 \HIGH CONDUCTIVITY TRANSPARENT INSULATOR TRANSPARENT ELECTRODE EE E 4 E JLAYER y ifififi'i' GROUP TWO 2 F E LAYER A E ELECTRODE X 3 P c LAYER \HIGH CONDUCTIVITY m E L LAYE R TRANSPARENT GROUP ONE A jg F E LAYER ELECTRODE I2 I I 0w CONDUCT-WHY L0 G 0' '|4 42 GROUP ONE E L LAYER l 4 F E LAYER =1 2 A E L LAYER GROUP Two 2.1 F E LAYE R I2 22 P c LAYER l E L LAYE R GROUP ONE 3 Q F E LAYER 6 FIG .3. v 2 3 48 it -E L LAYER E GROUP THREE 33 sz 2 P c LAYER so Q E L LAYER GROUP ONE L5 F E LAYER F d IJXENTOR 40 re ernow 38' I 62 M G 7 BY I VIEWING S |DE CHERNOW IMAGE FORMING SCREEN UT ILIZING ELECTROLUMINESCEN OTGCONDUCTIVE MATERIALS 2 Sheets-Sheet 1 HIGH CONDUCTIVITY ELECTRODE 36 ATTORNEY 'Oct. 31, 1967 F CHERNOW 3,350,506

IMAGE FORMING SCREE N UTILIZING ELECTROLUMINESCEN FERROELECTRIC AND PHOTOCONDUCTIVE MATERIALS Filed Oct. 28, 1963 2 Sheets-Sheet 2 E L LAYER PC LAYE \I Fi e .8. V2 INVENTOR h FIG .5. C

ATTORNEY United States Patent 3,350,506 IMAGE FORMING SCREEN UTILIZING ELECTRO- LUMINESCENT, FER ROELECTRIC AND PHOTO- CONDUCT-IV E MATERIALS Fred Chernow, Burlington, .Mass., iassignor to Electra-Tee Corp., West Caldwell, N.J., a corporation of Newdersey Filed Oct. 2.8, 19163, Ser. No. 319,458 12 Claims. (Cl. 178-73) This invention relates ,to image forming screen means, and more particularly to flat, two-dimensional image forming screens.

It is an object of this invention to provide a flat image forming screen having a plurality of condition-responsive coextensive layers in a predetermined relationship where by .a flying spot raster may be generated and then modulated by a video input signal to produce an image of the television type.

Another object of this invention is to provide a flat image forming screen having a plurality of condition-responsive coextensive layers, wherein each of the said layers comprises either an electroluminescent, photoconductive or ferroelectric layer, said layers being arranged in a novel sequence.

Still another object of this invention is to provide a fiat image forming screen comprising an optimally minimum number of component parts which occupies an optimally minimum amount of space.

Still another object of this invention is to provide a flat image forming screen which obviates the use of cathode ray tubes in television display means and provides an image screen having a substantial useful life.

Still another object of this invention is to provide a scanning system including a flat screen means having a plurality of condition-responsive coextensive layers and a plurality of function generators selectively supplying input functions .to said layers whereby a flying spot raster may be effected, and further wherein said raster may be selectively initiated in either of two orthogonal directions.

Yet another object of this invention is to provide a scanning system including a flat screen means having a plurality of laminated condition-responsive layers and a plurality of function generators selectively supplying input functions to said layers, said layers having complementary physical properties which are selectively disturbed by selective ones of said input functions such that adjacent areas of said image screen are progressively energized in a scan pattern determined by said input functions.

'These and other objects of this invention will become more fully apparent with reference to the following specifications and drawings which relate to several preferred schematic embodiments 'of the invention.

In the drawings:

FIGURE -1 is an enlarged schematic end view of the image screen of the present invention;

FIGURE 2 is anenlarged end view of the lower pair of condition responsive layers shown in FIGURE .-l with function generators connected in circuit therewith;

FIGURE 3 is a perspective including .-the lower condition-responsive layers and the three next-highest condidition-responsive layers of FIGURE 1 with function generators connected in circuit therewith;

FIGURE 4 is a perspective of all of the conditionresponsive layers of FIGURE 1 with function generators connected in circuit therewith;

FIGURE 5 is a graphic representation of the voltage versus time characteristics of the function generators of FIGURE 2;

FIGURE 6 is a field-position-time characteristic diagram for the combination of FIGURE 2; and

FIGURE 7 is an enlarged schematic end view of another embodiment of the present invention.

0nd and third electrodes 'ice Generally the structure of the present invention comprises three component groups of condition-responsive layers, the said layers being coextensively juxtaposed within the said groups, the said groups being selectively interconnected via coextensively juxtaposed transparent conductive-and/ or transparent insulating layers therebetween.

The system of the present invention which results in image formation from the above-definedstructure is completed by a plurality of function generators connected, respectively, across a face of and/ or transversely of each of .the groups of condition-responsive layers whereby a time varying electric field results in one or more directions in each of said condition-responsive layers.

The condition responsive layers are. of three classes of materials namely, photoconductive, hereinafter referred to as a PC layer; electroluminescent, hereinafter referred to as an EL layer; and ferroelectric, hereinafter referred to as an FE layer.

The use of ferroelectric and electroluminescent layer for producing an image forming screen are known in the prior art. The present invention is concerned With the type of EL-FE image forming screen in which a distributed bias is applied to the FE and is progressively varied so that a switching voltage which corresponds to the coercive field strength of the material is progress'ively moved across the FE material. At each point where the FE material switches from one polarity to another, it exhibits a relatively low reactance and provides a path for a relatively large voltage to be applied .to corresponding points of the EL material. The EL material responds to a certain voltage thereacross to produce light. The FE material, as shown in .the prior art, is a dielectric material having two stable polarity states and is referred to herein generically as a bistable dielectric material.

Referring in detail to the drawings, and more particularly to FIGURES 1 and 4, the image screen 10' is divided into three groups, namely, groups 1, 2 and 3, respectively.

Group 1 is located at the back side of the screen 10 and comprises a first low conductivity rectilinear planar base electrode 12 comprising the back side of the screen 10; a second rectilinear planar-electrode 14 parallel with and spaced from the first electrode 12 and being composed of a highly conductive transparent material; an PE layer '16 coextensive with said first planar electrode 12 intermediate said first and second electrodes 12 and 14, respectively and an EL layer 18 mutually juxtaposed and coextensive with said PE layer 16 and said second planar electrode .14.

Group 2 is stacked upon group 1 and comprises a PC layer 20 juxtaposed and coextensive with the said second electrode 14 ofgroup 1; a second FE layer22 juxtaposed and coextensive with said PC layer 20; and second 'EL layer 24 juxtaposed and .coextensive with said second FE layer '22; and a third rectilinear planar elect-rode 26; parallel with said first and second electrodes 12 and 14, respectively, said third electrode 26 being juxtaposedand coextensive with said second EL layer .24. The third electrode 26 is composed of a low conductivity transparent material for a purpose to be hereinafter more fully described.

Group '3 is stacked upon but separated from group 2 by means of a transparent insulating layer 28 which on one side thereof, is juxtaposed and coextensive with the said third electrode 26. Group 3 comprises a fourth rectilinear planar electrode 30 parallel with the first, sec- 12, 14 and 26, respectively, said fourth electrode 30 being juxtaposed and coextensive with said transparent insulating layer 28 and composed of a highly conductive transparent material; a second PC layer 32 juxtaposed and coextensive with said fourth electrode 30; a low conductivity opaque light barrier layer 33 juxtaposed and coextensive with said second PC layer 32; a third EL layer 34 juxtaposed and coextensive with said light barrier layer 33; and a fifth rectilinear highly conductive, transparent planar electrode 36 which, on one side, is juxtaposed and coextensive with said third EL layer 34 and which, on its other side, comprises the viewing side of the image screen 10.

Referring now to FIGURE 2, group 1 is energized by first and second function generators G1 and G2, respectively.

The first function generator G1 is connected across the length of the low conductivity first electrode 12, as indicated by the dimension L in the drawings, by means of first and second end terminals 38 and 40, respectively, located at opposite sides of the first electrode 12 on the dimension 1 These terminals may be of any suitable construction such as plated or otherwise deposited strips.

The second function generator G2 is connected on one side to ground and on its other side to the second terminal 40 at the first electrode 12. The output of the said second generator G2 is connected across the thickness dimension of the FE and EL layers 16 and 18, respectively, of group 1 by grounding a terminal 42 on the highly conductive second electrode 14, placing said electrode at a common potential with the said one side of the said second generator G2.

Referring now to FIGURE 3, group 2 is energized by third and fourth function generators G3 and G4, respectively, in a manner similar to that of group 1, the energization, however, being orthogonal to that of group 1 as will be hereinafter more fully described.

The third function generator G3 is connected across the low conductivity third electrode 26 by means of third and fourth end terminals 44 and 46, respectively, which are located at opposite edges of the said third electrode along a dimension perpendicular to the dimension L across which the first function generator G1 is connected.

The fourth function generator G4 is connected on one side to ground and on its other side to the fourth end terminal 46 on the third electrode 26, placing the said one side of the fourth generator G4 and the second electrode 14 at a common potential.

Referring again to FIGURE 4, all of the energization connections for groups 1 and 2 are shown as well as that for group 3. Group 3 is energized by a fifth function generator G5, which provides a modulating output function to be hereinafter more fully described.

The fifth function generator G is connected across the thickness dimension of group 3 with one side thereof connected to ground, the other side thereof connected to a terminal 48 on the fifth electrode 36, and by means of a terminal 50 on the fourth electrode 30 which is connected to ground, whereby the said fourth electrode 30 is placed at a common potential with the said one side of the fifth function generator G5.

Referring now to FIGURE 7, another embodiment of the invention comprising an image forming screen for modulated single variable or one-dimensional displays is effected by stacking groups 1 and 3 together such that the second electrode 14 and the fourth electrode 30* are merged in a single highly conductive and transparent common electrode 52 between the said groups.

Operation Referring first to FIGURES 2, 5 and 6, the operation of the basic scan generating means of the present invention will now be described.

Group 1 of the three basic groups of layers is adapted to generate a line of light perpendicular to the dimension L in the EL layer 18. This is accomplished by the interrelationship of the function signal voltages V and V respectively, created by the first and second function generators G1 and G2 and the hysteresis characteristic of the FE layer 16 when it is forced to switch from one polarity state to the other.

The generator G1 creates an electric field gradient along the dimension L by its connection across the low conductivity first electrode 12, whereby the field strength through the double layer comprising the PE layer 16 and the EL layer 18 varies as a function of position along the dimension L The sawtooth voltage V of the second function generator G2 is a sawtooth wave form with the same cycle 1- and half-cycle T/2 periods as the square wave function signal voltage V1 of the first function generator G1. Thus, the effect of the second function V2 is to create a time varying electric field through the double layer of group 1 which acts progressively to drive up the reference level of the field gradient created by the first function V1, generators G1 and G2 being synchronized.

The four curves shown in FIGURE 6 represent the electric field E across the thickness of the FE and EL layers 16 and 18, respectively, comprising the active layers of group 1, as a function of position along the dimension L x being the position variable along that dimension. The time sequence of the curves is (1), (2), (3) and (4), with the appropriate times (t) indicated on each curve, 6 being an interval small compared to 1- and comprising the time required for V to go from V1 to 0 or from 0 to V1.

The first function V1 is chosen such that where the position variable x=L the electric field through the layers of group 1 is equal to the coervice field (switching voltage) necessary to switch the polarization of the PE layer 16. Now, as the second function voltage V of the second generator G2 builds up progressively with time, the voltage gradient as shown in FIG. 6 increases causing the switching voltage to progress along the length of the PE layer from right to left. The progressive movement of the switching voltage causes a progressive switching of the PE layer.

The progressive achievement of a coercive field strength (switching voltage) along the dimension L causes a progressive switching of the polarity state of the FE layer 16 through all of the positions x along the said dimension. During the switching or change of state of the FE layer 16, the dielectric constant of the PE layer 16 increases in a substantial amount causing a corresponding redistribution of the voltage applied across the PE layer 16 and the EL layer 18 via the first and second electrodes 12 and 14. This increases the voltage drop across the EL layer 18 causing it to luminesce or light up brightly along a line perpendicular to the dimension L as a position x corresponding to the location of the discrete area in which the switching or change of state is at that instant taking place in the FE layer 16. Therefore, by applying the first and second functions V and V respectively, across the dimension L of the low conductivity first electrode 12 and between the first and second electrodes 12 and 14, respectively, and further, by properly selecting the final magnitude of the time varying voltage function V at the end of each half-cycle 7/ 2, a line of light may be generated in group 1, perpendicular to the dimension L which will sweep across the entire surface of the EL layer 18 between the terminal positions x=L and x=0. The frequency or rate of scan is determined by the frequency of the said first and second voltage functions V and V The first and second function generators G1 and G2, used in the manner set forth above with reversed polarities in the second half cycle, utilize the return half of the hysteresis loop characteristic of the FE layer 16 to effect a second trace of the line of light, thereby obviating a switching or change of state of the PE layer 16 which otherwise would be necessary to effect a flyback of the line. The reverse polarity voltage functions V and V are applied during the period from t=-r/2 second to 1:1 seconds, at which time one full sweep cycle of the line trace has been completed, the PE layer 16 being in the same condition as it was at t=0.

-' By utilizing both sides of the hysteresis loop'characteristics of the FE layer 16, the current capacity of the generators G1 and G2 is markedly reduced since the excessive currents required to effect a switching of the PE layer 16 during flyback are obviated.

Referring now to FIGURE 3, once the line of light has been generated in the EL layer 18, it is transmitted through the transparent second electrode 14 and impinges upon the PC layer 20 in group 2. The PC layer 20 becomes highly conductive in the region where the line of light strikes it, thereby creating a sweeping line of high conductivity across the PC layer on the dimension L In group 2, the third and fourth generators G3 and G4, correspond in function, respectively, to the first and second generators G1 and G2 of group 1. However, the said third and fourth generators G3 and G4 are so connected with respect to the second PE layer 22, second EL layer 24, and first PC layer 20 that the output signals thereof pass through all of these layers. Since the first PC layer 20 is of high resistivity except in the region corresponding to the line of light generated in the first EL layer 18, a second gradient and progressive or scanning increase thereof orthogonal to the dimension L is generated to scan in orthogonal relationship with the line or region of high conductivity, and because of the high resistivity of the first PC layer 20, a high voltage drop and hence coercive field strength sufficient to excite the second FE layer 22 and produce light in the second EL layer 24 is only effected across the latter two layers in the region of the said line of high conductivity This results in a point or spot of light in the region common to the high conductivity region and the orthogonally related second positionmodulated time varying field gradient.

Now, by making frequency of the voltage function of the fourth function generator G4 much greater than the frequency of the corresponding voltage function V of the second generator G2, the spot or discrete area of light formed in the second EL layer 24 in group 2 may be caused to scan entirely across the screen before the line of light in group 1 and consequently the line of high conductivity in the PC layer 20 of group 2, has moved a distance along the dimension L, which is greater than its own width.

Referring to FIGURES 1 and 4, once the flying spot has been generated in the second EL layer 24 of group 2, it is transmitted through the transparent third electrode 26, transparent insulator 28 and fourth transparent high conductivity electrode 30 and impinged upon the second PC layer 32, the latter comprising the lower active layer of group 3.

Group '3 comprises a modulating light amplifier which causes the degree of illumination produced in the third EL layer 34 to vary as a combined function of the initial intensity of the flying spot impinged upon the said second PC layer 32 and a superimposed modulation voltage function derived from the fifth function generator G5.

The flying spot creates a corresponding spot of high conductivity in the second PC layer 32, causing a redistribution of voltage applied across the said second PC layer and the third EL layer 34, via the fourth and fifth electrodes 30 and 36, respectively, whereby the said EL layer is subjected to substantially the full modulating voltage from the fifth generator G5 and is forced to luminesce in the same position as that of the conductive spot in the said second PC layer. By modulating the voltage output of the fifth generator G5, the brilliance of the flying spot in the third EL layer 34 may be modulated to provide the contrasts necessary to effect an image on said third EL layer of the screen 10 if the frequency of the scan and the luminescent memory of the luminescent third EL layer 34 is sufficient.

Thus, if the fifth generator G5 comprises a source of video signals properly synchronized with the sweep functions of the first, second, third and fourth generators,

6 be effected on the third EL layer 34 of the screen 10 which would be visible and viewed through the fifth transparent electrode 36.

Referring to FIGURE 7, the operation of group 1 is identical with that described in conjunction with the embodiments of FIGURES 1 through 6, such that a flying line scan is effected, the line of light generated in the first EL layer 18 in group 1 moving in a direction transverse its own width along the dimension L The fifth signal generator G5, in this embodiment, causes the PC-EL combination of group 3 to intensity modulate the scanning line of light generated in the EL layer 18 of group 1 and may, in itself, comprise the single variable tobe displayed on the EL layer 34 of group 3 as an intensity function. The intensity modulation is effected identically with that previously described herein for the embodiment of FIGURES 1 and 4.

As can be readily understood upon consideration of the foregoing specification and drawings, this invention provides a new and novel light line scanning means, a new and novel single variable display screen comprising a combination of a light line scanning means and a modulating light amplifier, a new and novel fiying light spot scanning means comprising a combination of first and second light line scanning means and a new and novel image generating screen comprising the said new and novel flying light spot scanning means in combination with a modulating light amplifier. The laminated structure of the present invention comprised of a plurality of unitary coextensive layers and the novel energization of the active ones of these layers by preselected voltage functions satisfies a long felt need in the art to provide a thin, flat television image forming means which occupies an optimally minimum space and has an optimally maximum useful life.

It is to be understood that the specific embodiments of the invention shown and described herein are for the purpose of example only and are not intended to limit the scope of the appended claims.

What is claimed is:

1. An image forming screen of the type comprising:

( a) an electroluminescent material of the type which produces a light when a threshold voltage is applied thereto,

(b) a bistable dielectric material of the type which decreases in impedance when switching from one stable state to the other stable state,

(c) said bistable dielectric material being connected to said electroluminescent material,

((1) means for providing a first voltage across the combination of said electroluminescent and bistable dielectric material which increases in absolute value in a first direction along said bistable dielectric material and varies periodically in polarity, and

(e) means for varying the level of said first voltage in synchronism with said first voltage periodicity whereby a voltage sufiicient to cause switching of said bistable dielectric material is moved along said bistable dielectric material in a direction parallel to said first direction and said electroluminescent layer gives off light in response to a redistribution of voltage which occurs when said bistable dielectric material switches.

2. An image forming screen as claimed in claim 1 wherein said bistable dielectric material is a ferroelectric material.

3. An image forming screen as claimed in claim 1 further comprising:

(a) a light amplifier positioned to amplify any light given off from said electroluminescent material, and

(b) means for modulating the brightness of the light produced by said light amplifier.

4. An image forming screen as claimed in claim 1 G1, G2, G3 and G4, respectively, a television image could 7 wherein said means for providing a first voltage comprises:

(a) a transparent electrode at reference potential con nected to said electroluminescent material,

(b) a resistor placed along a surface of said bistable dielectric material, and

(c) a first square wave voltage source connected between the ends of said resistor.

5. An image forming screen as claimed in claim 4 wherein said means for varying comprises:

(a) a sawtooth waveform generator for producing sawtooth waveforms alternating polarity every other period,

(b) the period of said sawtooth waveform coinciding with the period of said square wave voltage, and

(c) means connecting said sawtooth generator between one end of said resistance and said reference potential.

6. An image forming screen as claimed in claim 5 further comprising:

(a) a layer of photoconductive material,

(b) a thin layer of low conductivity opaque material placed on top of said photoconductor layer,

(c) a second electroluminescent layer placed on top of said thin layer,

(d) an electrode placed on top of said second electroluminescent layer,

(e) said photoconductor layer being placed on said electrode at reference potential, and

(f) means for connecting a modulated AC. voltage between said electrode at reference potential and said electrode on said second electroluminescent material.

7. An image forming screen as claimed in claim 6 wherein said bistable dielectric material is a ferroelectric layer.

8. An image forming screen as claimed in claim 5 further comprising:

(a) a layer of photoconductive material placed on said electrode at reference potential,

(b) a second layer of bistable dielectric material placed on said photoconductive material,

(c) a second layer of electroluminescent material placed on said second layer of bistable dielectric material, (d) a transparent resistive layer placed on said second electroluminescent material,

(e) means for providing a second voltage across the combination of said photoconductive, said second bistable dielectric, and said second electroluminescent layers which increases in absolute value in a second direction, substantially perpendicular to said first direction, and varies periodically in polarity, and

(f) means for varying the level of said second voltage in synchronis-m with said second voltage periodicity whereby a voltage sufficient to cause switching of said second bistable dielectric material is moved along said second bistable dielectric material in a direction parallel to said second direction and said second electroluminescent layer gives ofi light in response to a redistribution of voltage which occurs when said second bistable dielectric material switches.

9. An image forming screen as claimed in claim 8 wherein said means for providing a second voltage comprises:

(a) a second square wave voltage source connected between the ends of said transparent resistive layer, and

(b) said latter connection being substantially perpendicular to the connection of said first square wave voltage source. I

10. An image forming screen as claimed in claim 9 wherein said means for varying the level of said second voltage comprises:

(a) a second sawtooth wave-form generator for producing sawtooth waveforms alternating polarity every other period,

(b) the period of said second sawtooth waveform coinciding with the period of said second square wave voltage and being substantially different from the period of said .first square wave and sawtooth waveforms, and

(0) means for connecting said second sawtooth generator between said reference potential and one end of said transparent resistance.

11. An image forming screen as claimed in claim 10 further comprising:

(a) a transparent insulating layer placed on said transparent resistive layer,

(b) a transparent electrode placed on said transparent insulating layer,

(0) a photoconductive layer placed on said transparent electrode,

(d) a thin low conductivity opaque layer placed on said latter photoconductor layer,

(e) an electroluminescent layer placed on said opaque layer,

(f) a transparent electrode placed on said latter electroluminescent layer, and

(g) means for connecting a modulated AC. voltage between said latter two transparent electrodes.

12. An image forming screen as claimed in claim 11 wherein each of said bistable dielectric materials is a ferroelectric layer.

References Cited UNITED STATES PATENTS 2,922,986 l/196O Chynoweth 340-1732 2,964,646 12/1960 Helms SOT-88.5 3,126,509 3/1964 Pulvari 30788.5 X 3,249,804 5/1966 Aiken 315-169 JOHN W. CALDWELL, Acting Primary Examiner.

DAVID G. REDINBAUGH, Examiner.

P. SPERBER, I. M. HUGH, J. A. ORSINO,

Assistant Examiners. 

1. AN IMAGE FORMING SCREEN OF THE TYPE COMPRISING: (A) AN ELECTROLUMINESCENT MATERIAL OF THE TYPE WHICH PRODUCES A LIGHT WHEN A THRESHOLD VOLTAGE IS APPLIED THERETO, (B) A BISTABLE DIELECTRIC MATERIAL OF THE TYPE WHICH DECREASES IN IMPEDANCE WHEN SWITCHING FROM ONE STABLE STATE TO THE OTHER STABLE STATE, (C) SAID BISTABLE DIELECTRIC MATERIAL BEING CONNECTED TO SAID ELECTROLUMINESCENT MATERIAL, (D) MEANS FOR PROVIDING A FIRST VOLTAGE ACROSS THE COMBINATION OF SAID ELECTROLUMINESCENT AND BISTABLE DIELECTRIC MATERIAL WHICH INCREASES IN ABSOLUTE VALUE IN A FIRST DIRECTION ALONG SAID BISTABLE DIELECTRIC MATERIAL AND VARIES PERIODICALLY IN POLARITY, AND (E) MEANS FOR VARYING THE LEVEL OF SAID FIRST VOLTAGE IN SYNCHRONISM WITH SAID FIRST VOLTAGE PERIODICITY WHEREBY A VOLTAGE SUFFICIENT TO CAUSE SWITCHING OF SAID BISTABLE DIELECTRIC MATERIAL IS MOVED ALONG SAID BISTABLE DIELECTRIC MATERIAL IN A DIRECTION PARALLEL TO SAID FIRST DIRECTION AND SAID ELECTROLUMINESCENT LAYER GIVES OFF LIGHT IN RESPONSE TO A REDISTRIBUTION OF VOLTAGE WHICH OCCURS WHEN SAID BISTABLE DIELECTRIC MATERIAL SWITCHES. 